Multi-function day/night observation, ranging, and sighting device and method of its operation

ABSTRACT

A multi-function day/night observation, ranging, and sighting device includes a single objective lens and a single eyepiece lens and provides an image of a scene. The single objective lens leads to a visible-light first optical path and to an invisible-light second optical path. The invisible-light second optical path includes an image intensifier tube providing a visible image. The first-and second optical paths converge with visible images provided by each pathway being overlaid at a reticule plane. A single light path leads from the reticule plane to the eyepiece lens. A laser provides a pulse of laser light projected into the scene via the single objective lens, and the image intensifier tube is used as a detector for a portion of the laser light pulse reflected from an object in the scene in order to provide a laser range finding function. The device includes a light-emitting display visible through the eyepiece lens and providing ranging information superimposed over the image of the scene as seen by a user of the device. Methods of the device&#39;s operation are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the field of image-magnifying viewingdevices (i.e., telescopes) which can be used both in the day time toobtain a magnified view of a distant scene, and which can also be usedat night or under other conditions of low ambient lighting in order toview such a distant scene. The view of the distant scene is magnified,and at night is also intensified or amplified by use of an imageintensifier tube to provide a visible image when the scene is too darkto be viewed with diurnal vision. Accordingly, this invention relates totelescopes and other such viewing devices which may be used both in dayand at night for observation and surveillance.

The present invention also relates to laser range finding apparatus andmethod. Such laser range finding apparatus and methods ordinarilyproject a pulse of laser light into a scenes The laser light pulseilluminates objects in the field of view and is partially reflected fromat least one object in the scene whose distance from the observer is tobe determined. In order to select this one object, the device mayinclude a reticule and the laser light pulse may be of "pencil beam"configuration. The reflected portion of the laser light pulse isdetected at the device, and the transit time for the laser light pulseto travel to and from the object is used to calculate a range to theobject using the speed of light as a measuring standard.

This invention is also in the field of telescopic weapon aiming sightswhich provide a user with an aiming reticule, and which includeprovisions for bore-sighting the relative position of the reticule on ascene to the trajectory of a projectile. In other words, the telescopicdevice allows adjustments to place the reticule image on the viewedscene at the location where a bullet or other projectile will strike ata particular range.

2. Related Technology

A conventional day/night telescopic sight is known in accord with U.S.Pat. No. 5,084,780, issued Jan. 28, 1992 to E. A. Phillips. The Phillipspatent appears to teach a telescopic day/night sight which has severalalternative embodiments According to one embodiment set out in thePhillips patent, such a telescopic sight includes a single objectivelens behind which is disposed an angulated dichroic mirror. This mirrordivides light coming into the sight via the objective lens into twofrequency bands. Light of longer wavelengths (lower frequencies) isallowed to pass through the dichroic mirror to an image intensifiertube. This image intensifier tube operates in the conventional wayfamiliar to those ordinarily knowledgeable about night vision devices.That is, the image intensifier tube provides a visible image whichreplicates a dim image or an image formed by invisible infrared lightwithin the so-called near infrared . Thus, the longer wavelength bandwhich passed through the dichroic mirror includes the infrared portionof the spectrum and provides to the image intensifier tube thefrequencies of light to which the tube is most responsive.

The visible portion of the light entering the Phillips sight via theobjective lens is reflected by the dichroic mirror into an opticalsystem leading to a combiner and to an eyepiece. At the combiner, theimage provided by the image intensifier tube is superimposed on theimage from the visible-light channel of the sight, and the resultingcombined image is presented to a user of the sight via the eyepiece.

A possible disadvantage of the Phillips sight as described above is thatthe angulated dichroic mirror can introduce both parallax, astigmatism,and color aberrations into the image provided to the user. Thus, slightmovements of the sight may cause the user to experience some shifting ofthe image along a line parallel with the angulation of the mirror, whilethe image does not shift along a line perpendicular to this angulation.In other words such an angulated dichroic mirror may result it theslight jiggling inherent in a hand-held telescope or weapon sightamplifying the apparent movement of the image in at least one direction.This effect can be disconcerting for the user of the device.

Other versions of the Phillips sight use a separate objective lens forboth the day channel and the night channel of the sight. These versionswould not appear to suffer from the same possible parallax problemdescribed above with respect to the versions using the dichroic mirror.However, the versions of Phillips sight with two objective lenses sufferfrom an increased size, weight, and expense because of the additionaloptics and larger housing required to mount and protect these optics.

In each case with the sight disclosed by Phillips, the optical channelsfor the night sight and the day sight are laterally offset relative toone another. These two offset optical channels are parallel, and theimage from these channels is combined for presentation at the eyepiece.However, in each case, the sight taught by Phillips requires separatelaterally offset optical channels, and presents the problem of correctlyand precisely superimposing the image from these two channels for theuser of the sight.

Another consideration with the Phillips sight is the mechanism and sizeof housing required for effecting windage and elevation adjustments ofthe reticule. Some versions of the Phillips sight use a reticule plate,while others use an injected reticule (i.e., provided by a projector fora lighted reticule "dot" which is superimposed on the image of theviewed scene). In each case, the objective lens of the device receives alarger scene image (i.e., field of view) than is provided to the user,and the reticule is moved about within this field of view in order toprovide windage and elevation adjustments. However, it is oftendesirable for the user of such a sight to perceive no apparent change inthe centering of the reticule on the field of view. This results in asmaller imaged field of view with a centered reticule pattern movingabout in a larger field of view provided by the objective optics.Understandably, optical systems of this type suffer from increased sizeand weight because of the larger objective optics.

Yet another disadvantage of sights of this conventional type is that themechanism for moving the reticule is inherently located near the rear ofthe sight. This location for the reticule mechanism results in thehousing of the sight being undesirably large at a location whereclearance must be provided for the action mechanisms of many weapons.

Another conventional day/night weapon sight is known in accord with U.S.Pat. No. 5,035,472, issued Jul. 30, 1991 to Charles L. Hansen. The U.S.Pat. No. '472 appears to disclose a sighting device including a numberof dichroic reflectors, which divide the incoming light into spectralbands. The visible one of the spectral bands passes to an eyepiece forviewing by a user of the device. Another of the spectral bands of lightpasses to an image intensifier tube. A visible image provided by thisimage intensifier tube then passes to the eyepiece. Yet another spectralband passes to a focal plane array device, such as to a CCD. The CCD isassociated with a display device, such as a CRT. The image from the CRTthen passes to the user via the eyepiece.

The device disclosed in the U.S. Pat. No. '472 appears not to providelaser range finding. No provisions appear to be made for a reticuleusable in sighting by use of this device. Focusing and adjustment of areticule position for windage and elevation also appear not to beaddressed by the U.S. Pat. No. '472.

Conventional laser range finders have also been known for a considerabletime. One exemplary version of such a device is known as the MELIOS.This device uses viewing optics, a laser having a projection opticalsystem, and a detector having a separate receiving optical system, alldirected at a scene in which an object is located having a range to bedetermined. In operation, the laser provides a pulse of laser light, andthis is projected into the scene via the projection optics. This laserlight illuminates the object, and a portion of the laser light isreflected back toward the device. Part of the reflected laser lightreturning to the device is captured by the receiving optical system, andis directed to a detector. The device includes a timer starting when thelaser light pulse is transmitted and stopping when the returning laserlight is detected. A calculator portion of the device uses the elapsedtime from transmission of the laser light pulse until detection of thereturning reflected laser light to calculate the distance to the object.

Another conventional laser range finder is known as the Commander'sViewer Sight. This device uses a catadioptric optical viewing system,and places separate optics for projecting and detecting the laser lightin the central obscuration of the viewing optical system. Thus, theviewing optics and laser range finder optics (i.e., projector anddetector optics) are coaxial in this sight, but they are neverthelessseparate optical structures.

SUMMARY OF THE INVENTION

In view of the deficiencies of the conventional day/night observation,sighting, and ranging devices it is an object for this invention toavoid one or more of these deficiencies.

Further to the above, it is an object for this invention to provide aday/night telescopic observation and sighting device which has a daychannel and a night channel which receive light from a scene via asingle objective lens.

Furthers it is an object for this invention to provide a day/nighttelescopic sight which includes a laser range finder projecting laserlight into a scene via the same singular objective lens which is used toreceive light from the scene.

Still furthers an objective for this invention is to provide such aday/night observation and sighting device in which an image intensifiertube serves as a detector of returning reflected laser light, as well asproviding a visible image of the scene for viewing by the user of thedevice.

Yet another objective is to provide such a day/night observation andsighting device in which the same objective lens which is used toobserve the scene, and though which laser light is projected into thescene for laser range finding, is also used to receive the reflectedlaser light to provide for detection of this laser light.

Still another objective for this invention is to provide such aday/night observation and sighting device which allows the user of thedevice to manually adjust image brightness and image intensifier tubegain under at least one operating condition.

Another objective for this invention is to provide such a day/nightobservation and sighting device which provides a daytime operating modein which the brightness of the image provided to the user of the deviceis controlled by a fixed repetition rate of gating of operating voltageto an image intensifier tube of the device.

Accordingly, the present invention provides a day/night imaging devicecomprising- an objective lens receiving light from a distant scene; aneyepiece lens providing an image of the distant scene; an imageintensifier tube receiving light via the objective lens and responsivelyproviding a visible image available at the eyepiece lens; a power supplycircuit selectively providing in a first mode of operation a variabledifferential voltage to a microchannel plate of the image intensifiertube, and in a second mode of operation the power supply circuitalternatingly supplying differing voltage levels in a duty cycle to aphotocathode of the image intensifier tube; whereby brightness of animage provided by the image intensifier tube to a user of the device iscontrolled selectively by operating the power supply circuitalternatively in one of the first and second modes of operation.

According to another aspect, the present invention provides a day/nightviewer apparatus, the apparatus comprising- an image intensifier tubeproviding an image having a brightness level; a power supply circuit forthe image intensifier tube, the power supply circuit including a pair ofalternative means for controlling brightness of the image provided bythe image intensifier tube, one of the alternative means beingoperational in a day-time imaging mode, and the other of the alternativemeans being operational in a night-time imaging mode, respectively; theone alternative means of the pair including a voltage converter circuitproviding a differential voltage on a microchannel plate of the imageintensifier tube, and a control circuit responsive to a current levelfrom the image intensifier tube to control image brightness of the tubeby selective reduction of the differential voltage; the otheralternative means of the pair including a pair of voltage sourcecircuits, one of the pair of voltage source circuits providing anegative voltage and the other providing a voltage which is positiverelative to a first face of the microchannel plate, a switching networkalternating connection of the photocathode of the image intensifier tubebetween the pair of voltage source circuits in a duty cycle.

Still additionally, the present invention provides according to anotheraspect a method of operating a viewing device in order to provide animage of controlled brightness both during day-time and duringnight-time modes of operation, the method comprising steps of providingthe device with an image intensifier tube, and directing light from ascene to the image intensifier tube; causing the image intensifier tubeto responsively provide a visible image; providing a power supplycircuit for the image intensifier tube, and including in the powersupply circuit a pair of alternative circuit means for controllingbrightness of the image, making one of the alternative means operationalin a day-time imaging mode, and making the other of the alternativemeans operational in a night-time imaging mode, respectively; includingin the one alternative means a voltage converter circuit providing adifferential voltage on a microchannel plate of the image intensifiertube, and a control circuit responsive to a current level from the imageintensifier tube to control image brightness of the tube by selectivereduction of the differential voltage; including in the otheralternative means a pair of voltage source circuits, one of the pair ofvoltage source circuits providing a negative voltage and the otherproviding a voltage which is positive relative to a first face of themicrochannel plate, and alternating connection of the photocathode ofthe image intensifier tube between the pair of voltage source circuitsin a duty cycle.

An advantage of the present invention resides in its combination withina single device of day and night (i.e. night vision) viewing devices, alaser range finder, and a weapon sight with both a reticule and ranginginformation superimposed over a target scene. The combined simultaneouspresentation of day or night views, ranging information, and a sightingreticule allows a user of the device to very quickly sight on a targetor provide target position information (i.e., bearing and range relativeto the user). Uses for this device in the military and in lawenforcement are apparent.

Additional objects and advantages of the present invention will beapparent from a reading of the following detailed description of one ormore preferred exemplary embodiments of the invention taken inconjunction with the appended drawing Figures, in which like referencecharacters denote like features or features which are analogous instructure or function, as will be explained.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 provides an exterior view of a telescopic day/night observation,sighting, and ranging device embodying the present invention being usedto observe a distant scene as well as to obtain a range to an object inthis scene;

FIG. 1a provides an exterior perspective view of the device seen in FIG.1 viewed from the opposite perspective;

FIGS. 2a and 2b together provide a diagrammatic longitudinalrepresentation, partially in cross section, of the internal structuresof the device seen in the preceding drawing Figures;

FIGS. 3, 4, 5, and 6 respectively provide an assembly view inlongitudinal cross section, an exploded perspective view, an axial crosssectional view from the underside of the device, and a longitudinalcross sectional view, all of associated portions of the device seen inthe preceding drawing Figures;

FIG. 7 is a fragmentary diagrammatic perspective view of yet anotherportion of the device seen in the preceding drawing Figures;

FIG. 8 provides a spectroscopic diagram of the light transmission andlight reflection performance of a feature of the device as seen in FIG.7;

FIG. 9 is a graphical presentation of a voltage-versus-time wave formwhich may be experienced within the device seen in the preceding drawingFigures;

FIG. 10 provides a schematic representation of a control systemarchitecture for the device;

FIG. 11 provides a depiction of a view (i.e., of a distant scene andsuperimposed reticule and ranging information) which may be seen by auser of the device;

FIG. 12 is a fragmentary cross sectional view similar to a portion ofFIG. 2a, but showing particulars of an alternative embodiment of theinvention; and

FIG. 13 is a schematic and diagrammatic representation of a particularembodiment of a power supply and control circuit architecture for adevice embodying the present invention.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS OF THE INVENTION

An overview

Viewing FIGS. 1 and la in conjunction, a telescopic day/nightobservation, ranging, and sighting device (the "device") is depicted asit may be used by a user 12. In this case, the device 10 is mounted to arifle 14, and the user 12 is using the device to view a distant scene16. It will be understood that the device may be used alone withoutbeing mounted to a rifle 14, or to any other weapon. On the other hand,the device 10 is not limited to use as a sight for a rifles and may beused for sighting a variety of weapons. Accordingly, it is seen that thedevice 10 is not limited to this or any other particular use, and otheruses for the invention as embodied in device 10 and in its various otherembodiments will be apparent to those ordinarily skilled in thepertinent arts.

In the distant scene 16 are personnel 18, and in the instant case, inaddition to being able to observe the scene 16 and personnel 18, theuser 12 would like to know the range to these personnel. The personnel18 may be moving about and are only generally indicated in the scene 16,but in order to obtain a range to this scene 16 the user may select anynumber of convenient stationary objects in the scene 16 for rangingpurposes. By obtaining a range to any one of the stationary objects, anacceptably accurate range to the personnel is also obtained. In thesituation depicted, the housing structure 20 would probably be selectedby the user 12 for ranging purposes. Alternatively, the user 12 mayrange to a vehicle, tree, or other natural feature, such as an exposedrock or rock formation, for example, to obtain a range to the scene 16.In the scene 16, a variety of such objects are depicted and areavailable to the user 12 for ranging purposes.

In order to range to the scene 16, upon a command from the user 12, thedevice 10 sends out a pulse 22 of laser light. This laser light pulse isof very short duration, and is not visible to the unaided human eye.However, the laser light pulse 22 does illuminate a portion of the scene16, generally in the center of this scene as viewed by the user 12 viathe device 10. Some part of the laser light pulse will be reflected fromone or more objects in the scene 16 back toward the device 10, as isindicated by arrow 24. The returning laser light 24 is detected at thedevice 10, and range information is provided in a selected form to theuser. For example, the range information may be presented to the user innumerical form superimposed over the scene 16 as seen through the device10.

Considering the device 10 now in greater detail, it is seen that deviceincludes a housing 26 which is offset along its length, and which is ofstepped outer diameter. These specific features of construction areparticular only to the embodiment of the invention depicted in FIGS. 1and 1a, and the invention is not so limited The housing 26 at a forwardend includes an objective lens 28. The term "forward" as used here hasreference to the direction toward an object or scene to be viewed by useof the device, while the terms "rear" or "rearward" refer to theopposite direction toward a user of the device In this case, the device10 has only a single objective lens, and this objective lens 28 is usedto receive light from the scene 16, as is indicated by the arrows 28a.The light 28a will include visible light during day-time use of thedevice 10. Also, the light 28a may include light both in the visibleportion of the spectrum, as well as light in the red end of the visiblespectrum and in the near-infrared portion of the spectrum during bothday-time and night-time use of the device 10, as will be furtherappreciated in view of the following.

It will be noted that objective lens 28 is also used as a projectionlens for projecting the pulse of laser light 22 into the scene beingviewed by the user 12. The invention is not limited to laser light pulse22 projecting into the scene 16 via lens 28, and this should be viewedas a convenience and feature of the particularly illustrated anddescribed embodiment of the invention. In addition, the objective lens28 is used to receive the returned portion of the laser light pulseafter reflection from one of more of the objects in the scene 16.

At its rear end, the device 10 includes an eyepiece 30 into which theuser 12 peers to obtain a magnified (i.e., telescopic) view of theobject or scene toward which the device 10 is directed. The eyepiece 30is rotational, as is indicated by arrow 30a, in order to allow the user12 to focus this portion of the device. The housing 26 also provides abattery housing portion 32 having a removable cap 34 allowingreplacement of a battery (not shown in FIGS. 1 or 1a) which is housed inthe portion 32. A power switch 36 allows the user 12 to turn on and offa night vision function of the device 10, as will be further described.Also, other operational switches, generally indicated with numeral 38and to be further described below allow the user to initiate a laserrange finding (LRF) operation, and to control other functions of thedevice 10, as will be more fully explained.

Along the body 26 are located three adjustment knobs generally indicatedwith the numerals 40, 42, and 44. Knob 40 provides for objectivefocusing of the device, while knobs 42 and 44 respectively provide forwindage and elevation adjustment of a field of view of the scene 16relative to a fixed aiming reticule of the device 10, all of which willalso be explained. A pair of recessed levers 46 and 48 respectivelyprovide for selection of spatial and optical filters to be used in thedevice 10 during observation and laser range finding operationsdependent upon the conditions of use for the device, as will beexplained.

Turning now to FIGS. 2a and 2b and considering this structure ingeneral, it is seen that the device 10 includes a number of lenses incolor-corrected groups arranged along a bifurcated and convergentoptical pathway leading from the objective lens 28 to the eyepiece 30.That is, an image presented at eyepiece 30 may be considered to havetraveled along either one or both of the branches of the opticalpathway. One branch of this pathway includes an image intensifier tube50 so that the image presented at eyepiece 30 from this branch of theoptical pathway is derived from light admitted to this pathway viaobjective lens 28, but is a replica image.

As those ordinarily skilled in the pertinent arts will know, when suchan image intensifier tube is supplied with electrical power ofappropriate voltage and current levels by a power supply circuit 52drawing its electrical power from a battery stowed in the batteryhousing portion 32 under control of the on/off switch 36. Undernight-time or other conditions of low ambient lighting level, the tube50 will provide a visible image replicating an image in low-levelvisible light or in invisible near-infrared light. However, the imageintensifier tube 50 can also be used in day time to provide an image,and can be used under marginal lighting conditions of dusk or earlydawn, for example, to supplement an optical image provided along theother branch of the device 10. The image intensifier tube can also beused in full daylight to provide imaging functions and other functionsto be described more fully below.

Generally, those ordinarily skilled in the pertinent arts will know thatimage intensifier tube 50 includes a transparent window portion 50abehind which is a photocathode responsive to photons of light from ascene to liberate photoelectrons in a pattern replicating the scene, amicrochannel plate which receives the photoelectrons and which providesan amplified pattern of secondary emission electrons also replicatingthis scene, and a display electrode assembly. Generally, this displayelectrode assembly has an aluminized phosphor coating or phosphorscreen. The electron pattern impacting on this screen creates a visibleimage replicating the scene. A transparent window portion 50b of thetube conveys the image from this output electrode assembly (or "screen")outwardly of the tube so that it can be presented to the user 12.

As will be appreciated by those skilled in the art and also viewing nowFIG. 2, the individual components of image intensifier tube 50 are allmounted and supported in a tube or chamber having forward and reartransparent plates (i.e., defining the transparent windows into and outof the tube) cooperating to define a chamber which has been evacuated toa low pressure. This evacuation allows electrons liberated into the freespace within the tube to be transferred between the various componentswithout atmospheric interference that could possibly decrease thesignal-to-noise ratio. The tube 50 is operated by a power supply 52drawing electrical power from the batteries in battery housing 32.

Typically, power supply 52 will apply an electrostatic field voltage onthe order of 200 to 800 volts to the photocathode in order to allow itto liberate photoelectrons in response to incident photons. Preferably,a constant voltage level of 800 volts is provided by the power supply 52for connection to the photocathode of the image tube 50. As will befurther explained, this constant voltage is controllably, and possiblyvariably, gated on and off of connection to the photocathode in order tocontrol brightness of the image presented to user 12, both to allow alaser range finding function to be carried out by the device 10, andpossibly to allow the user 12 of the device to manually control thebrightness level of the image or the gain provided by the imageintensifier tube 50 of the device.

After accelerating over a distance between the photocathode and theinput surface of a microchannel plate, the photoelectrons entermicrochannels of the microchannel plate. The power supply 52 maintains aselected voltage differential across the opposite faces of thismicrochannel plate (i.e., across conductive electrode coatings carriedon these faces) so that the photoelectrons are amplified by emission ofsecondary electrons to produce a proportionately larger number ofelectrons upon passage through the microchannel plate. This amplifiedshower of secondary-emission electrons is also accelerated by arespective electrostatic field generated by power source 52 to furtheraccelerate in an established electrostatic field between the second faceof the microchannel plate and the screen. Typically, the power source 52produces a field on the order of 3,000 to 7,000 volts, and morepreferably on the order of 6,000 volts during imaging operations inorder to impart the desired energy to the multiplied electrons. Duringlaser range finding operations of the image tube 50 this applieddifferential voltage across the microchannel plate is preferablyincreased to a "high gain" level, as will be explained. This amplifiedshower of electrons falls on the phosphor of the screen to produce animage in visible light.

Considering now the optical elements of the device 10, it is seen thatthe objective lens 28 admits light from the scene to a lens doublet 54a,54b. These lenses project the light to an afocal lens set includinglenses 56a-56d. Light exiting lens 56d is substantially collimated. Thelight from lens set 56a-56d is directed to a movable focus cell,generally indicated with the arrowed numeral 58. This focus cell 58includes lenses 58a-58f, and is effectively a second smaller andrelatively movable objective lens set in the device 10. As will beexplained further below, the focus cell 58 is movable axially forfocusing, as is indicated by arrow 60; is movable vertically forelevation adjustment, as is indicated by arrow 62, and is movablelaterally for windage adjustment, as is indicated by arrow 64 (thedot-centered circle and cross respectively indicating the head and tailof a focus cell movement arrow perpendicular to the plane of FIG. 2).The objective lens sets 28, 54, 56, and focus cell lenses 58cooperatively effect a first inversion of the image of the scene. Lightexiting lens 58f is focused to a distant image plane, and as will befurther described is to be divided into two spectral bands. Thus, thelight exiting lens 58f is focused to two separate image planes dependentupon the wavelength band of the light. Understandably, the longerwavelengths of light will be focused to an image plane at thephotocathode of the image intensifier tube 50. The shorter wavelengthsof light (i.e., visible light 28a(v)) are focused to an image plane tobe identified below.

Next, the light which has entered device 10 via objective lens 28encounters a prism assembly 66 which is best seen in FIG. 7. The prismassembly 66 includes a first and a second prism members 66a and 66b,which have an angulated interface 66c. As is seen, the interface 66c isangulated so that incoming light from the objective lens 28 will bereflected downwardly. However, interface 66c is provided with areflective-transmissive dichroic coating, indicated with arrowed numeral66d. Also, a central oval portion of the dichroic coating 66d isprovided with an especially spectrally-selective dichroic coatingportion 66d', as is further described below. Importantly, the dichroiccoating 66d selectively passes longer wavelengths of light (i.e., fromabout the blue portion of the visible spectrum through the red portionand on into the near-infrared portion of the spectrum). As will befurther explained, the spectrally-selective coating portion 66d' has aweighted average transmissibility of wavelengths to which the imageintensifier tube 50 is responsive of about 70%. Thus, the longerwavelengths of light (indicated with arrows 28a(ir) pass through theprism assembly 66, and are focused through the front transparent windowof the image intensifier tube 50 onto the photocathode of this tube,viewing FIG. 2 once again and recalling the description above of theoperation of the image intensifier tube. In other words, the lens groupfrom and including objective lens 28 through the lens 58f have an imageplane at the photocathode of the image intensifier tube 50. In responseto this light 28a(ir), the image intensifier tube 50 can provide avisible image.

However, a significant portion of the light in the visible portion ofthe spectrum indicated by arrows 28a(v)! is reflected from the dichroiccoating 66d at interface 66c, and passes downwardly through anotherplate-like prism assembly 68, which is a portion of the prism assembly66. Prism assembly portion 68 includes two plate-like members 68a and68b, which cooperatively define an interface 68c angulated at 45 degreeswith respect to the vertical and directed laterally of the device 10. Onthis interface 68c is located another coating 68d of thespectrally-selective coating material used for area 66d'. The visiblelight wavelengths (28a(v)) substantially pass through this interface andthrough the coating 68d. The light passing downwardly through portion 68reflects from a beam splitter mirror 70 having a first-surfacereflective-transmissive surface 70a. Thus, the light 28a(v) is reflectedfrom surface 70a rearwardly of the device 10 toward eyepiece 30.

Behind the beam splitter mirror 70 (i.e., toward the eyepiece 30, andviewing FIGS. 2a and 2b once again) is it seen that device 10 includes alens group 72 including lenses 72a-72e, and having two image planes. Inthe direction toward the eyepiece 30, the lens group 72 has an imageplane at the location indicated by dashed line 74 and effects a secondinversion of the image of the scene, so that an erect image is presentedat plane 74. On the other hand, in the direction away from eyepiece 30,the lens group 72 has an image plane located at the plane of a face 76aof a light emitting diode (LED) display 76. The function of this displaywill be further described below.

Next, light passing toward the eyepiece 30 encounters a combiner prism78, having a first prism portion 78a and second prism portion 78b,cooperatively defining a reflective-transmissive interface 78c. Lightfrom the prism assembly 70 (and from the display 76 as well, as will beexplained) passes through this prism assembly, passing through the imageplane 74, and to the eyepiece optics which are generally indicated withnumeral 80 and which include eyepiece lens 30. It will be noted thatthese eyepiece optics 80 are non-inverting.

However, at the plane 74 is disposed a reticule plate 82. This reticuleplate includes a selected reticule pattern, such as a cross-hair withminute of angle (MOA) dots (as will be explained with reference to FIG.11), for purposes of allowing the device 10 to be used in sighting aweapons The image of the reticule pattern is seen by user 12superimposed on the image of the scene 16. Further considering theeyepiece optics 80, it is seen that these optics include lenses 80a-80d,and eyepiece lens 30. As noted above, relative rotation of the housingportion 30a moves the eyepiece optics group 80 axially of the housing 26and focuses the eyepiece lens group at plane 74.

Considering now the image presented by image intensifier tube 50 atwindow 50b, it is seen that this image is inverted because of the firstinversion of the image effected by the objective lenses, as explainedabove. The image intensifier tube 50 is of non-inverting type, and alsoprovides an inverted image at window 50b. A relay lens group, indicatedwith numeral 84 includes lenses 84a-84d, has an image plane at plane 74,and effects a reversion of the inverted image presented by tube 50 sothat an erect image is presented to the user 12 at plane 74. The imagefrom image intensifier tube 50 is overlaid at the image plane 74 withany visible-light image (i.e., formed by light 28a(v)) so that the user12 can see these two images superimposed on one another if both arepresent. At night and under other low-light conditions, thevisible-light image will be fully or substantially absent, and the userwill see the image from the image tube 50. Light from the relay lensgroup 84 is directed by a mirror 86 downwardly into combiner prism 78,to be reflected from the interface 78c toward the eyepiece 30.

Stated differently, the visible light image provided by light 28a(v),and the image presented by the image intensifier tube 50 in response tothe light 28a(ir) are superimposed on one another at the image plane 74,and are viewable each alone or together at the eyepiece 30 (i.e., theuser is looking at image plane 74). Thus, under day-light conditions,the device 10 may be used using only visible-light imaging, or maycombine visible light imaging with the image provided by the imageintensifier tube 50, if desired (i.e., even in full day-lightconditions, as will be explained). At night-time and under otherlow-light conditions, the device 10 provides night vision using theimage from the image intensifier tube 50.

Further to the above, it will be noted that the light focused to theimage plane 74 by lens groups 72 and 84 can also pass through the prism78 in a downward direction, with the light from lens group 72 beingreflected partially from interface 78c. Light from lens group 84partially transmits through the interface 78c. Thus, yet another imageplane is present at a front face 87a of a light responsive electronicimaging device 87. The imaging device 87 may include, for example, acharge coupled device. Other types of electronic imaging devices may beemployed at this image plane (i.e., at the plane indicated at 87a) inorder to capture electronically an image using the device 10. As aresult, the device 10 can provide an image via an electrical interfaceindicated by conductor 87b.

Moving Focus Cell for Windage/Elevation Adjustment

Turning now to FIGS. 3-6 in conjunction with one another, andconsidering FIG. 3 first, it is seen in this Figure that the focus celllens group 58 is movable in the vertical direction in order toaccomplish a relative movement of the scene 16 as imaged by the device10 relative to the fixed reticule 82. The displacement of the focus cell58 is in the vertical direction for elevation adjustment, but it will beunderstood that the focus cell 58 is movable laterally of the device 10(recalling arrow 64) for windage adjustment.

Moving the focus cell 58 from its centered position effectively movesthe image of the portion of the scene 16 seen through the device 10relative to the fixed reticule 82. This movement is accompanied by avery slight off-axis shift in angulation of the image, which is reducedaccording to the magnifying power of the focus cell lens group 58.Importantly, because the device 10 effectively moves the imaged portionof a scene relative to a fixed reticule, the reticule always remainscentered in the view provided to the user 10. As will be addressedfurther below, lateral movements of the focus cell lens group 58simultaneously move or "steer" the projected laser light 22 on scene 16so that this projected laser light beam corresponds at its center withthe point of aim indicated by reticule 82.

Viewing FIGS. 3-6, it is seen that the focus cell lenses 58a-58f arecarried in a tubular focus cell body 88. The focus cell body 88 is ofstepped tubular configuration, and includes a large diameter portion 88ahaving an outer surface 88b, and a reduced diameter portion 88c passingthrough an aperture 90a in a focus cell cross slide member 90. The largediameter portion and smaller diameter portion of the body 88cooperatively define a radially extending and axially disposed guidesurface 88d. Similarly, the cross slide member 90 defines a pair ofopposite radially extending and axially disposed guide surfaces 90b and90c, only one of which is visible in FIG. 5. The focus cell body 88carries a pair of diametrically opposite axially projecting pins 92(only one of which is visible in FIG. 4--both being visible in FIG. 3) ,which are slidably received into vertically extending guide slots 94(again, both being visible in FIG. 3) formed on the surface 90c of crossslide member 90.

Extending perpendicularly to these guide slots described above, thecross slide member 90 defines a pair of diametrically opposite andparallel guide surfaces, each indicated with the numeral 90d. A portionof the smaller diameter portion 88c of body 88 is externally threaded,and an internally threaded retainer collar 96 is threaded onto the body88 so that a radially extending and axially disposed surface 96aslidably engages the surface 90b. A locking ring 98 is also threadedonto the portion 88c of the body 88 in order to lock the collar 96 inplace. Consequently, the body 88 is guided on cross slide member 90 bysliding engagement of surfaces 88d/90c, and 90b/96a, with the pins 92 inslots 94 constraining the body 88 to relative vertical motion.

In order to provide for relative horizontal motion of the cross slidemember 90 (and of body 88), the device 10 includes a cross slide mount100, best seen in FIG. 3. This cross slide mount 100 defines a pair ofdiametrically opposite, parallel and laterally extending guide surfaces10a, slidably engaging and supporting the cross slide member 90 byengagement with surfaces 90d. In order to effect lateral movement of thefocus cell group 58 so as to move the image of scene 16 in horizontaland vertical relative directions (i.e. for windage and elevationadjustments), the focus cell body 88 and cross slide member 90 eachcarry a respective one of a pair of radially outwardly extending,rigidly attached, and orthogonally disposed threaded stems, eachindicated with the numeral 102. One of the stems 102 extends parallel tothe slots 94 and is attached to body 88, while the other is parallel toguide surfaces 90d and is attached to cross slide member 90. Each of theguide stems 102 will be seen to effect independent windage or elevationadjustment on the one of the members 88 or 90 to which it attaches.

In FIG. 3, only one of the guide stems 102 is visible, the other extendsperpendicularly to the plane of this Figure (viewing FIG. 4 for anillustration of the orthogonal relationship of the stems 102). However,the adjustment mechanisms for each stem are essentially the same so thatdescription of one suffices to describe both. FIGS. 3 and 4 show thatthe stems 102 are each threadably received into an internally threadedbore 104a of a hat-shaped rotatable nut member 104. The nut member 104includes a radially projecting flange portion 104b, carrying a pair ofdiametrically opposite pins 104c (only one of which is fully visible inFIG. 4). The pins 104c are each drivingly received slidably into arespective slot 106a of a rotational drive disk member 106 having acentral aperture 106b. At aperture 106b, the disk 106 is received overthe hat-shaped nut member 104. Furthers this drive disk member 106includes another pair of slots 106c, which are located perpendicularlyto the slots 106a. In each of the slots 106c is drivingly received oneof a respective diametrically opposed pair of pins 108a carried on aradial flange portion 108b of a knob core member 108.

Viewing FIG. 3, it is seen that this knob core member 108 isrotationally carried by the housing 26 by use of an apertured basemember 110, having an aperture 110a into which the knob core 108rotationally is received This base member 110 carries an aperturedreaction disk 112 (part of which is seen in the exploded perspectiveview of FIG. 4) by which the nut member 104 is rotationally constrainedfrom axial movement between these two members. Thus, it is seen that thenut member 104 is trapped rotationally between the reaction disk 112 andthe base member 110 along with the drive disk 106 and knob core member108. The disk member 106 effectively provides a Scotch-yoke type ofrotational and translational drive mechanism between the knob core 108and the nut member 104, allowing for relative eccentricity between thesetwo rotational members while providing a rotational driving relationshipbetween them. Because of the driving relationship between the knob core108 and nut member 104, rotation of the knob core 108 is effective torotate the nut member and translate stem 102, regardless of theeccentricity which may exist between the members at a particular time.

Captively carried rotationally on the knob core member 108 is arelatively rotational knob member 114, which carries a locking lever116. When the locking lever 116 is manually pivoted from its illustratedposition outwardly about 90°, an eccentric portion 116a of the leverbinds with and grips the knob core 108 to allow manual rotation of theknob core. Recalling FIGS. 1 and 1a, it is seen that in each instancethe respective knob core 108 and knob member 114 cooperatively make upthe knobs 42 and 44 seen on the outside of the device 10 for respectivewindage and elevation adjustments. In this way, a user of the device 10can effect manual windage and elevation adjustments of the focus cell58.

FIG. 6 shows a click-adjustment mechanism of the knob core 108 which isgenerally indicated with the numeral 108c. This click adjustmentmechanism both restrains the knob core 108 against unwanted movements,and also provides both a tactile "feel" and audible "click" indicativeof the extent of manual movements effected to the focus cell 58 by theuser of the device 10. Viewing FIGS. 3 and 6 in greater detail, it isseen that the base member 110 defines an annular recess 110a, having amultitude of radially inwardly disposed ridges or lands 110b, definingradially inwardly disposed grooves 110c there between. In this case,both the lands 110b and grooves 110c number 62 In order to provide aclick-adjustment mechanism 108c of finer resolution than 1/62 of arotation of the knob core member 108, a collar portion 108d of the coreextends into the recess 110a, and defines three circumferentiallyregularly spaced apart slot-like apertures 108e. One of threecylindrical detent members 118 is closely movably received into each ofthe apertures 108d, and each is urged radially outwardly toward a groove110c by an annular spring member 120.

However, because the number of grooves of the click adjust mechanism108c (i.e., 62) is not evenly divisible by 3, only one of the detentmembers 118 can be in a groove 110c at any time. The rotational positionerror between the other two detent balls and their closest groove willbe (62-60)/3, (i.e., 2/3 of the width of one land 110b) with thepositional error being evenly shared by each of the two detent memberswhich are not received in a groove In other words, one detent ball isreceived in a groove 110c, and the other two are each 1/3 of the widthof a land 110b away from being received into a groove. Dependent uponthe direction of rotation of the knob core 108, one of the detentmembers 118 will require 1/3 of a land width to reach its groove in theparticular directions while the other will require 2/3 of a land widthof movement. As a result, the click adjustment mechanism 108c provides aresolution of about 1/180 rotation per "click" for the knob core 108.

Axial Focusing Movement of Focus Cell 58

Furthers FIGS. 4 and 5 show that the focus cell 58 is also movableaxially (recalling arrow 60 of FIG. 2) by axial sliding movement of thecross slide mount 100 along the interior surface 26a of housing 26. Thisaxial movement of the focus cell lens group has the effect of adjustingthe focus of light at the image planes (i.e., at the photocathode of theimage intensifier tube 50 and at the plane 70b noted above),compensating for the variable distance to the scene 16 being viewed. Inother words, the focus cell 58 is moved axially in order to assure thatincoming light is focused both on the photocathode of the imageintensifier tube 50, and at the image plane 70b. From an infinity-focusposition for the focus cell 58, the axial movement of the focus cell 58required in order to accommodate all other closer distances for focusingof the device 10 need only be about 0.050 inch or less. It will berecognized in this respect that the device 10 is intended to focus frominfinity to as close as about 50 yards. Focusing of device 10 atdistances closer than about 50 yards is not necessary.

In order to provide such axial movement of the focus cell 58, thehousing 26 provides a boss 122 having a bore 122a into which a pin 124is pivotally received. Outwardly, the housing 26 may have a slightprotrusion 122b for boss 122. The pin 124 is secured to and pivotallysupports a somewhat curved lever 126. The lever 126 has another pin 128spaced from pin 124 on the centerline of the body 88 and receivedpivotally and slidably into a transverse slot 130 defined by cross slidemount 100. The lever 126 curves to wrap partially around the body 88,and at a distal end portion 126a includes a slot 126b extendinggenerally parallel with the pins 124 and 128. Movably received into theslot 126b is a pin 132a carried by the internal rotational portion 132drivingly connected to the focus knob 40.

In view of the above, it is easily seen that rotation of knob 40 drivesthe portion 132 in rotation, and that pin 132a gyrates, driving thelever 126 in oscillatory pivotal movement These pivotal movements of thelever 126 are translated into axial movements of the cross slide mount100 by pin 128 operating in slot 130. Thus, the user 12 can adjust thefocus of the focus cell lens group 58 to account for differing distancesto the scenes 16 which the user may want to view.

Laser Injection for Laser Range Finding

Returning to a consideration of FIG. 7, it is seen that the prismassembly 66, including portion 68, is associated with a laser lightprojection assembly 134. This laser light projector assembly originatesa laser light pulse, which when projected outwardly into the scene 16via the objective lens 28, becomes pulse 22. In order to provide a pulseof laser light projected from the prism assembly 66 forwardly throughthe objective lens 28, as is indicated with arrowed numeral 22a, theassembly 134 includes a laser diode 136, which when energized provides apulse of laser light indicated with numeral 22b. Preferably, this laserlight pulse has a wavelength of about 820 nm, which is in the infraredportion of the spectrum and is not visible to humans. The pulse of light22b is projected through a stationary lens 138 toward a selectivelymovable lens 140. Lens 140 is illustrated in solid lines in FIG. 7 inits position to provide a "pencil beam" of projected laser light aspulse 22, recalling FIGS. 1 and la and the discussion concerning objectsin the scene 16 which may be different in reflection of laser light andwhich may be selected for laser ranging in the scene 16. The lens 140 isselectively moveable under control of the user 12 between the positionin solid lines in FIG. 7 and an alternative position shown in dashedlines in this Figure.

In the dashed line position of lens 140 in FIG. 7, the lens 140 causesthe pulse of light 22 to have a divergence of about 2 degrees. Thiscauses the laser light pulse 22 to illuminate a portion of the scene 16which varies in size according to the distance between the device 10 andthe scene 16. Understandably, by selection of the area of the sceneilluminated by the laser light pulse 22 in view of the magnitude of thereflection from the object to which laser range finding is beingperformed, the user 12 can choose a combination of object(s) reflectionintensity, and area of illumination giving the best possible laser rangefinding results.

The light of laser light pulse 22b is projected by lens 140 into theprism member 68a, and reflects from coating 68d upwardly to prismassembly 66. In the prism assembly 66, the laser light pulse 22b isincident upon the coating portion 66d, which for this wavelength oflight provides an almost perfect reflection of about 99 percent.Consequently, the laser light pulse 22b is directed forwardly, and exitsthe prism assembly 66 as laser light pulse 22a, as noted above. Viewingnow FIG. 8, it is seen that the coating portion 66d (including portion66d') provides a nearly perfect reflection at the shorter wavelengths ofvisible light which must be reflected from this coating downwardly topass to eyepiece 30. At the longer infrared wavelengths, the coating 66dhas a low magnitude of reflection, and has a transmissibility weightedover the wavelengths to which the image intensifier tube 50 isresponsive of about 70%.

Further, viewing the ray trace of FIGS. 2a and 2b, it is seen that asignificant portion of the light which is focused at the image tube 50passes around the portion of interface 66c where the area of coating66d' is located. Accordingly, each area of the photocathode of the imagetube 50 will receive sufficient light that a significant shadow is notcast by the coating portion 66d'. Considered from an optical analysisapproach, the light received in the center of the image tube will beabout 91% of the possible light level were the coating 66d' not presentIn other words, the image provided by image tube 50 does not have ashadow or darkened area because of obscuration from coating portion66d'.

Again, at the longer light wavelengths centered around the 820 nmwavelength for laser light pulse 22, it is seen in FIG. 8 that thecoating 66d' has a magnitude of reflection which averages better than 80percent. Accordingly, the laser light pulse 22b from laser diode 136 isreflected from the coating 68d at interface 68c, and from coating 66d'at interface 66c, to be projected forwardly as pulse 22a (viewing FIG.7) and to become pulse 22 when it is projected from the objective lens28 into the scene 16.

Further considering this projection of pulse 22, it is seen that thelaser light 22b/22a has a path outwardly of the device 10 through thefocus cell group 58 and through the other lenses leading to and throughobjective lens 28 which is opposite to the incoming light from the scene16. In view of the description above of how movements of the focus celllens group 58 in the lateral directions (i.e, X-Y movements) areeffective to move the viewed scene as perceived through the objectivelens, it will be understood that these movements of the focus cell lensgroup simultaneously move the projected laser light 22 in the scene 16.During manufacture of the device 10, the point of projection of laserlight 22 is aligned with the center of the scene 16 (i.e., with thecenter of the reticule pattern seen in FIG. 11). In this way, a user ofthe device can select an object with which to perform a laser rangefinding operation by setting the reticule pattern on this object andcommanding a LRF operation.

Additionally to the above, as the user of the device 10 makes windageand elevation adjustments of the device to account for variations inmounting of the device on the weapon, and for ballistic differences inthe ammunitions and projectiles employed, these adjustmentssimultaneously "steer" the laser range finding light 22 in the scene 16.In other words, the projected laser light 22 always coincides withreticule 82.

Imaging using Image Intensifier Tube 50

Further to the above, it will be recalled that although the device 10may provide to a user an image entirely in visible light received byobjective lens 28, the alternative mode of operation is imaging by useof image intensifier tube 50, either alone (i.e., as a night visiondevice), or as an adjunct to the visible-light image. To this end, thepower supply circuit 52 is provided in order to operate the imageintensifier tube 50. This power supply circuit provides for a constantvoltage level (preferably of -800 volts) to be provided to thephotocathode of the tube 50, and to be gated on and off in a duty cyclein order to control the brightness of the image provided by the tube 50.This duty cycle may be variable and may be automatically controlled (aswill be seen), or may be manually controlled. This aspect of control ofthe brightness level of the image provided by tube 50 may be controlledby switches 38, one of which may serve as a "brightness increase" slewswitch, and another of which may serve as a "brightness decrease" slewswitch. Alternatively, an analog type of manual control for brightnessmay be provided on the outside of housing 26 where it is accessible tothe user 12. Such an analog control may take the form of, for example, arotational knob which by its rotational positions controls thebrightness of the image from tube 50.

Under use conditions of comparatively high brightness, but which arestill too dim to provide a good image by natural light alone, the userof the device 10 can supplement the natural light image provided by thedevice 10 by also operating the image intensifier tube 50. Under theseuse conditions, the image tube 50 may have a lower brightness level.Conversely, on a dark night, the image tube may be operating with a highbrightness level on the other hand, during day-time imaging, the imageintensifier tube may have its brightness level turned completely down.In other words, the duty cycle gating of constant -800 volts to thephotocathode of the tube 50 may be as low as 1×10⁻⁴ % This allows theimage tube 50 to provide an image in full day light, and to still beused as a sensor for laser range finding operations, as will be furtherexplained.

During day-time uses of the device 10 with image tube 50 turned on, theuser will most preferably employ an optical band-pass notch filter (tobe further described below). Such a filter has the advantage ofsignificantly decreasing or removing wavelengths of light from thatlight reaching image tube 50 other than right around the wavelengthselected for laser light 22. In this case, that wavelength is preferably820 nm. Even with such a filter introduced into the optical pathwayleading to the tube 50, the duty cycle of the tube may be turned down bythe user because the day-time scene is so rich in photons. The imagetube 50 can still provide a supplemental image from the light which doesreach it, but its response during laser range finding operations isconsiderably improved because of an improved signal to noise ratio.

Accordingly, it is seen that the duty cycle setting for the tube 50 isvariable, and may be at a low setting at a time when the user 12 wantsto perform a laser range finding operation.

Image Intensifier Tube Operation and Laser Range Finding Operation

Recalling the above, it will be seen that the user 12 may want toperform a laser range finding (LRF) operation using the device 10, andfurther may want to perform this LRF operation at a time when the dutycycle of the image intensifier tube 50 has been turned down by the user.In order to allow the brightness level adjustment for the imageintensifier tube 50 the power supply 52 provides a constant voltagelevel, preferably about -800 volts, which can be supplied to thephotocathode of the tube 50. Further, this power supply circuit gatesthis constant voltage level on and off of connection to the photocathodeat a constant selected frequency in a duty cycle. This duty cycle may bevariable or may be a selected constant value of duty cycle. The dutycycle level at which the constant voltage level is connected to thephotocathode of the tube 50 largely controls the brightness level of theimage provided by this tube (gain at the microchannel plate also has aneffect, as those ordinarily skilled will appreciate).

As pointed out above, the duty cycle for gating of the photocathode ofimage tube 50 may be varied by use of manual controls available to theuser of the device 10. For example, in response to manipulation of theslew switches noted above, the user may control brightness for the tube50. Preferably, the duty cycle frequency is 50 Hz in order to avoid anyvisible flicker in the image provided to the user 12 as a result of thebrightness control function.

Conversely, it should be kept in mind that when the duty cycle for imagetube 50 is 100%, the image intensifier tube 50 provides its maximum gainand maximum brightness for the image provided by this tube.Alternatively, the user 12 may select a lesser brightness depending onthe use conditions for the device 10 and the user's preferences bycommanding the duty cycle to be a lower value (i.e., less than 100% andas low as 1×10⁻⁴ %) by use of slew switches 38.

Now, viewing FIG. 9 it is seen that the portion 142 depicts a voltagegating wave form at the photocathode of the image intensifier tube 50which may apply either when the user 12 has turned down the brightnessof the tube 50 to some selected level, or which may represent a fixedduty cycle for the device 10 (for example, under day-time conditions).In the depicted case, the duty cycle is about 20%, which is merelyexemplary. The point is that the duty cycle is less than 100% to controlthe brightness of the image provided by tube 50. As is seen in theportion 142 of this graph, the voltage wave form includes a peak 144substantially at -800 volts indicating the connection of thephotocathode to the constant voltage level provided by power supply 52Following each peak 144 is an interval 146 of open-circuit voltage decaybecause the power supply circuit 52 opens connection of the photocathodeto the -800 volt supply, and voltage decays at a naturalcapacitor-discharge open-circuit rate. The magnitude of thisopen-circuit voltage decay is not great because the time interval isshort (i e., about 1/50th second for a 50 Hz frequency of duty cyclegating).

The power supply 52 in this instance is placing charge on a virtualcapacitor existing within the image intensifier tube 50 between thephotocathode and a microchannel plate of the tube. Next in each dutycycle as is indicated at 148, the power supply 52 connects thephotocathode to a constant relative-positive voltage level of about +30volts to effect a "hard turn off" of the photocathode. In other words,when connected to the relative positive voltage level, the photocathodeof the tube 50 is not responsive to photons of light to releasephotoelectrons in the tube. Preferably, this constant positive voltagelevel is about +30 volts relative to the front face of the microchannelplate in the tube 50. Because the tube has a time interval in each dutycycle during which it is not responsive to photons of light, thebrightness of the image provided by the tube 50 is decreased.

However, it will be noted that when the brightness and gain of the tube50 are turned downs the tube is also not providing its bestamplification in its prospective use as a sensor during laser rangefinding operations. Considering now FIGS. 9 and 10 together, it is seenthat the device 10 includes a laser range finding control circuit 150which at a microprocessor portion 152 receives a LRF control input fromthe user 12 via a switch 38 commanding the device 10 to perform a laserrange finding operation. In response to this LRF control input, thecontrol circuit 150 commands the power supply 52 to switch thephotocathode of the image intensifier tube 50 momentarily to the +30volts. This connection is indicated on FIG. 9 at 154, and is followedafter a selected time interval by connection of the photocathode to the-800 volts constant level provided by the power supply 52 for asubsequent time interval. This connection is indicated at 156 on FIG. 9.In the interval while the photocathode is connected to the +30 voltslevels the control circuit 150 provides an input to the laser diode 136via a laser power supply 158. The laser diode 136 responsively providesthe pulse of laser light 22b, which will become the pulse 22 projectedvia the objective lens 28 into the scene 16, as described above. Asensor 160 senses the pulse 22b, and provides a starting command to atimer 162.

The laser light pulse 22 is projected into the scene 16 as describedabove during the time interval after the photocathode of the imageintensifier tube 50 has been momentarily connected to the +30 volt levelfrom power supply 52. More particularlyl, the sequence of these eventsincludes shut down of oscillators 185 and 210, simultaneously withgating "off" of the photocathode of the image intensifier tube 50. Atthis same time, the microchannel plate of the image intensifier tube 50is switched to a high gain voltage level from MCP multiplier 188. Next,after a time interval of about 3 ms, the photocathode of the imageintensifier tube 50 is gated back "on" to the voltage level frommultiplier 186a. Next, after about 200 ms time interval, which isnecessary to "settle" the voltage level on the photocathode, the laserfires, and detector 160 detects the firing of the laser pulse and startstimer 162. After a short time interval which is necessary for the laserlight pulse to travel into and be partially reflected from objects inthe scene, the image intensifier tube 50 detects the pulse of reflectedlaser light and provides the signal necessary to stop timer 162 (i.e.,by connection 224 into amplifier 222).

In the time interval for return of the reflected laser light pulse, thecontrol circuit 150 provides an input command to an actuator 164. Theactuator 164 moves a spatial filters 166 into the light path (i.e., thepath for light 28a(ir)) between prism 66 and image intensifier tube 50.Possibly, two or more alternative spatial filters may be provided (i.e.,with differing sized of apertures), the selection of a particular onebeing dependent upon the position of lever 46. These spatial filters areessentially opaque blocking plates or shutters which define a centralaperture allowing reflected laser light to be returned to the imageintensifier tube from a selected central portion of the scene 16. Thesize of the portion of the scene 16 from which reflected laser light isreceived at tube 50 is dependent upon the size of the aperture in thespatial filter 166. For example, one of two alternative spatial filters166 may have an aperture of about 2 mm., while the other may have alarger aperture of about 12 mm.

Also, dependent upon the position of lever 48, an optical filter 168 maybe manually moved into the light path between prism 66 and imageintensifier tube 50. The optical filter 168 is a notch-transmissiontype, and transmits light substantially at the 820 nm wavelength of thelaser diode 136 (i.e., the wavelength of pulse 22) while partiallyblocking wavelengths other than this. Again, during day-time laser rangefinding operations, use of the optical filter 168 assists in filteringout other adjacent wavelengths of infrared light which may be rich inthe day-time scene, and thus improves the signal to noise ratio for theimage intensifier tube 50 in its mode of operation as a sensor for laserrange finder operation and also for imaging in day time.

Further, as is described above the returning laser light 24 reflectedfrom an object in the scene 16 is received by image tube 50 after thephotocathode has been connected to the -800 volt level (i.e., after timeinstant 156 of FIG. 9) and is very responsive to the returning laserlight. The connection to the -800 volt level indicated at 156 ismaintained for a sufficient time interval to insure that the returninglaser light pulse is received by the tube 50 while the photocathode ishighly responsive to photons. Further, the microchannel plate of theimage tube 50 has a voltage differential applied across it which makesit have a high gain level. As may be appreciated, the microchannel platefor imaging purposes may have a differential voltage applied which isless than the full high-gain differential voltage level. This may be thecase, for example, because viewing conditions are bright, or because abright source of light is present in the viewed scene. Regardless of thereason for the microchannel plate of the image tube having less than thehigh-gain level of voltage differential applied, when a LRF operation iscommanded, this differential voltage across the microchannel plate ischanged to a high-gain level substantially simultaneously with theapplication of the high-response voltage to the photocathode (i.e., atmoment 156 in FIG. 9).

Considered again, it is seen that in response to the reflected portion24 of the laser light pulse 22, the tube 50 experiences an electronpulse which provides a current flow from the screen and is sensed by aconnection through the power supply 52 into timer 162. The timer thusstops, with the interval of its operation measuring the time requiredfor light to travel to and from the scene 16. This measured timeinterval is read by microprocessor 152 and the distance to the scene iscalculated using the speed of light as a measuring standard. Themicroprocessor 152 then provides a range output via the display 76. Asmentioned above, the display provides an image which shines though thereflector 70 and combiner prism 78 and is visible to the user 12 ineyepiece 30.

As FIG. 9 depicts, after the connection of the photocathode of the imagetube to the -800 volt level in anticipation of the receipt of thereturning laser light pulse 24, and after a sufficient interval toinsure reception of the reflected laser light pulse, the power supply 52then resumes the gating operation indicated at 142', which is acontinuation of what ever gating operation had been going on prior tothe LRF operation in order to control image brightness and gain of thetube 50 for the user of the device 10. After the LRF operation, thespatial filter is also withdrawn from the light path by actuator 164.

FIG. 11 provides a representative example of the image provided by thedevice 10, which includes the reticule image 82a provided by reticuleplate 82, and range information 76b provided by LED display 76. As isseen on FIG. 11, the LED display 76 also provides (if applicable) anilluminated indicator 170, which will be blinking if the batteries ofthe device 10 are running low on power. Also, optionally, the device 10may include an external infrared spot light illuminator 172 (best seenin FIG. 1a) which projects a beam of infrared light 172a into the scene16 in order to provide illumination under extremely dark conditions.That is, during such extremely dark conditions as may exist within atunnel or inside of a building basement without windows, not even theimage intensifier tube 50 will provide an image without somesupplemental infrared light illumination. Under these conditions, theuser of the device 10 may turn on the illuminator 172, and theilluminator warning indicator 174 seen in FIG. 11 will remind the userthat this illuminator is on. Because the infrared light provided by theilluminator 172 is also visible to others having night vision equipmentand may reveal the presence and position of the user 12, suchsupplemental illumination is generally used only intermittently.

FIG. 12 provides a fragmentary view similar to a portion of FIG. 2a ofan alternative embodiment of the device 10 In order to obtain referencenumerals for use in describing this alternative embodiments featureswhich are the same or which are analogous in structure or function tofeatures described or depicted above, are referenced on FIG. 12 usingthe same numeral used above, and increased by one-hundred (100). Not allfeatures having a reference numeral mentioned below are seen in FIG. 12In cases where a feature not seen in FIG. 12 is referred to, the featureof FIGS. 1-11 having this numeral (i.e. minus 100) is indicated ViewingFIG. 12, it will be understood that a device 110 includes an objectivelens 128 admitting light to a lens double 154a and 154b (none of thesebeing shown in FIG. 12). The lenses 128 and 154 pass light to an a-focallens group including lenses 156a-156d. Collimated light provided by thelens group 156 is received by a movable focus cell lens group 158.However, in contrast to the embodiment depicted and described above, thefocus cell lens group 158 is movable only axially for focusing, and isnot at all movable laterally or vertically of the sight 110 for windageand elevation adjustment In order to provide for movement of the imagereceived via the objective lens 128 relative to the reticule plate ofthe device 110, the device includes two pairs of relatively rotatableRisley prisms, respectively indicated with numerals 180, and 182. Eachprism in each set of prisms is selectively counter rotatable relative tothe other prism in the set, and each prism set has a null position inwhich light enters and leaves the prism set in rays which are paralleland without offset from one side of the prism set to the other.

However, as the prisms in each prism set 180 or 182 are counter rotatedrelative to one another, the light traversing the prism set is off setalong a particular axis. The prism set 180 has its null positionarranged so that relative rotation of the prisms in this set results ina lateral offset of the light traversing this prism set. This prism set180 is connected to the windage adjustment knob 142 (not seen in FIG.12) to relatively rotate the individual prisms of this set in counterrotation with the particular direction of counter rotation dependentupon which way the knob 142 is rotated. Consequently, the image providedvia objective lens 128 is moved in a lateral (i.e., windage adjustment)direction.

Similarly, the prism set 182 is connected to the elevation adjustmentknob 144 to relatively rotate in opposite directions dependent uponwhich way the elevation adjustment knob is turned by the user of thedevice. As a result, when the elevation adjustment knob is rotated theimage received via objective lens 128 is moved in a vertical (i.e.,elevation adjustment) direction. Because each set of Risley prisms 180and 182 is independently adjustable (i.e., counter rotatable) withouteffect on the other set of prisms, the windage and elevation adjustmentseffected by a user in the device 110 have no effect on one another.Also, because the Risley prisms 180 and 182 are disposed in collimatedlight space between the afocal lens set 156 and the focus cell lens set158, none of the windage, elevation, or focus adjustments of the device110 has any affect on the others (the latter adjustment being effectedby axial relative movement of the focus lens groups 158--recalling thedescription above).

Turning now to FIG. 13, an exemplary circuit diagram for a power supplyand control circuit 150 for device 10 is depicted. In this drawingFigure, the photocathode (PC), microchannel plate (MCP), and outputelectrode (i.e., the screen) are indicated with reference numerals 50a,50b, and 50c, respectively. Considering FIG. 13, it is seen that thecircuit 150 includes a power source, which in this case is illustratedas a battery 184 Recalling the description above, the battery 184 may behoused in portion 32 of the housing 26. Considered generally, thecircuit 150 includes an oscillator 185 associated with a transformerprimary winding indicated with character T1. This transformer has othersecondary windings indicated at various locations in FIG. 13 forproviding power within the circuit and for receiving feedback. Theseother windings of transformer T1 are also indicated with the samereference characters Oscillator 185 is controlled by a regulator circuit185a receiving a control signal from a feedback circuit 185b with anassociated feedback winding of transformer T1.

Circuit 150 also includes three voltage converters or multipliers,respectively indicated with the numerals 186, 188, and 190, each havinga transformer secondary winding in association, as is seen in FIG. 13.The voltage multiplier 186 for the photocathode 50a actually includestwo separate voltage converters providing respective differing voltagelevels, and indicated with the numerals 186a and 186b. Preferably,voltage converter 186a provides a voltage level of about -800 volts,while voltage converter 186b provides a level of about +30 voltsreferenced to the voltage level provided at a first face of themicrochannel plate 50b, as will be seen. The voltage converter 188provides a differential voltage across the opposite faces of themicrochannel plate 50b. That is, this voltage differential is appliedacross surface conductive electrode coatings on these faces of the MCP50b, as those skilled in the pertinent arts will understand.

A tri-stable switching network 192 switches controllably betweenalternative positions either conducting the photocathode 50b to voltagemultiplier 186a, to voltage multiplier 186b, or to an open circuitposition, all via the conductive connection 192a. In other words, theswitching network 192 alternatingly connects the photocathode 50b of thetube 50 to a constant voltage source at about -800 volts, or to aconstant voltage source at about +30 volts relative to the front face ofthe microchannel plate, or to an open circuit condition, as will befurther seen. The open circuit interval of time employed in the presentembodiment between connections of the photocathode 50b to the twovoltage sources 186a and 186b is used for purposes of energy efficiency,and is optional. A duty cycle gating control 194 controls the switchingposition of the switching network 192, and receives as inputs a gatingtrigger timing control signal from a gating timing generator 196 via aday/night switch 196a, and a control signal via a conductor 198 from aLRF control logic unit 200. During day-time operation of the device 10,the switch 196a is closed, and the gating timing generator 196 controlsvoltage gating to the photocathode 50a to effect a fixed duty cycleduring imaging operations of the image intensifier tube 50. However,this gating timing control can be temporarily superseded by operation ofthe LRF control logic unit 200 during a LRF operation, as will be seen.

As will also be seen, during night-time operations of the image tube 50for imaging, the circuit 150 provides a non-gated operation of thephotocathode 50. Under such night-time non-gated operating conditions,an automatic brightness control (ABC) circuit 202 receives on conductor202a a feedback input indicative of screen current from screen 50c, andon conductor 202b provides a control input to a summing junction 204.This summing junction 204 also receives an input from a feedback circuit206 responsive to the voltage applied to microchannel plate 50b byvoltage converter 188. The summed inputs to junction 204 provide aninput to a regulator circuit 208 controlling an oscillator 210associated with a transformer indicated with the character T2. Thistransformer has other winding also indicated on FIG. 13 with thereference character T2.

Oscillator 210 receives power from battery 184, so this battery appearstwice, on FIG. 13, although it will be understood that this is just aconvenience of schematic illustration, and not an indication thatmultiple battery power supplies are required for the device 10.

During night-time operations of the device 10 for imaging, the ABCcontrol circuit 202 provides a reduction in the voltage differential onMCP 50b provided by voltage converter circuit 188 in response to thelevel of screen current sensed by connection 202a. This decrease inmicrochannel plate differential voltage reduces the gain of themicrochannel plate 50b, and is effective to reduce the brightness of theimage provided by the image tube 50. This type of ABC function isgenerally conventional and will be understood by those skilled in thepertinent arts without further explanation. However, it is important tonote that the LRF control logic unit 200 has a control output viabranched conductor 212 to both oscillators 185 and 210. In the case ofoscillator 185, this circuit is shut down during a LRF operation, andany reduction in voltage differential effected on MCP 50b for purposesof ABC is temporarily interrupted also for a LRF operation.

Further considering FIG. 13, it is seen that the circuit 150 includes amanual LRF command input device (i.e, a push button 38 for example,which is available to user 12) by which the user can command the deviceto perform a LRF operation. This input device provides an input to LRFcontrol logic unit 200, which responsively provides the outputsdescribed above, and also provides an output to laser driver 216. Thislaser driver 216 powers laser diode 136 to provide laser pulse 22b. Asensor 160 detects the moment of beginning for laser light pulse 22b,and provides a "timer start" input to a high speed timer 162. This timer162 responsively starts an interval time running, which will be ended inresponse to a "timer stop" signal provided by an amplifier 222. Theamplifier 222 has a connection by conductor 224 with the output currentfrom screen 50c of the image tube 50 and will provide the "timer stop"command in response to the electron pulse occurring when the reflectedportion 24 of the laser light pulse 22 arrives at image tube 50. Theresulting time interval for light to travel to and from the object inthe scene is provided to range calculator 220, which uses the speed oflight as a measuring standard and drives the display 76 to provide therange information as noted on FIG. 11. It will be noted that the LRFcontrol logic unit 200, timer 162, and calculator 220 may be implementedin the microprocessor 152 explained above with reference to FIG. 10. Forthis reason a dashed-line box is illustrated on FIG. 13, and indicatedwith numeral 152.

Having considered the structure of the circuit 150, further attentionmay now be given to its operation, and the cooperation of this circuitwith the operation of the image intensifier tube 14 to provide imagingboth in night-time and day-time conditions, as well as to provide LRFoperations under both of these conditions. As will be seen, the circuit150 may provide for a fixed day-time duty cycle, which is selected whenswitch 196a is closed, and may also provide for the user to adjust thegating duty cycle of the image tube to control brightness manuallyduring day-time uses of the device 10. This manual adjustment ofbrightness is provided by an optional duty cycle control circuit 226,which is responsive to a manual input device 228 to provide a duty cyclevariation command to the gating timing generator 196. A default value ofduty cycle which is applied in day-time operation of the device 10 willbe provided by the gating timing generator 196 in the absence of acommand for another value of duty cycle. In response to an input fromthe user 12, which may be provided by use of switches 38 for example,the user may be allowed to provide a command input to the gating timinggenerator 196 via duty cycle control circuit 226 to vary the duty cycleof the image tube 50, and thus to vary the brightness of the imageprovided by the tube 50 to the user in day-time conditions.

In each case, regardless of whether the image tube 50 is operating innight-time mode (i.e., with image brightness being controlled by circuit202 using the method of reducing the voltage differential across themicrochannel plate), or is operating in day-time mode (i.e., either witha fixed or manually-adjusted duty cycle--with image brightness beingcontrolled by the method of connection of voltages from sources 186a and186b to the photocathode 50a in a duty cycle); as mentioned above, whena LRF operation is commanded the image tube is converted momentarilyfrom its imaging function to a LRF sensor function. Upon the completionof the LRF function, the tube returns to the same imaging modepreviously existing Particularly, when the user commands an LRFoperation, the brightness control function of for the tube is suspended.Oscillators 185 and 210 are shut down, and the positive voltage levelfrom voltage converter 186b is momentarily applied to the photocathode50a in anticipation of the laser pulse 22b. When this laser pulse doesoccur, the image tube 50 will be unresponsive to any laser light backscattered in the device 10 because it has been subjected to a "hard turnoff". Next, full voltage from voltage converter circuit 186a is appliedto the photocathode 50a to place it in a high-response conditionpreparatory to receipt of pulse 24. Also, the voltage differentialacross microchannel plate 50b is increased to a high-gain level.

In view of the above, it is seen that when the reflected light pulse 24is received at the tube 50, an electron pulse occurs, which is sensed atconductor 224, and results in stopping the timer 162 to measure thelight-transit interval to and from the object selected for ranging. Therange information is provided to the user on display 76 (seen in FIG.11); and the device 10 then reverts to its previous imaging operation(with the previously used image brightness controls being restored)until the next LRF command is provided by the user.

While the present invention has been depicted, described, and is definedby reference to particularly preferred embodiments of the invention,such reference does not imply a limitation on the invention, and no suchlimitation is to be inferred. The invention is capable of considerablemodification, alteration, and equivalents in form and function, as willoccur to those ordinarily skilled in the pertinent arts. The depictedand described preferred embodiments of the invention are exemplary only,and are not exhaustive of the scope of the invention. Consequently, theinvention is intended to be limited only by the spirit and scope of theappended claims, giving full cognizance to equivalents in all respects.

I claim:
 1. A day/night imaging device comprising:an objective lensreceiving light from a distant scene; an eyepiece lens providing animage of the distant scene; an image intensifier tube receiving lightvia said objective lens and responsively providing a visible imageavailable at said eyepiece lens; a power supply circuit selectivelyproviding in a first mode of operation a variable differential voltageto a microchannel plate of the image intensifier tube, and in a secondmode of operation said power supply circuit alternatingly supplyingdiffering voltage levels in a duty cycle to a photocathode of the imageintensifier tube; whereby brightness of an image provided by the imageintensifier tube to a user of the device is controlled selectively byoperating said power supply circuit alternatively in one of said firstand second modes of operation.
 2. The device of claim 1 furtherincluding manually-adjustable means for allowing a user of the device toadjust said duty cycle to apply in said second mode of operation.
 3. Thedevice of claim 1 further including a voltage converter circuitproviding said differential voltage to said microchannel plate of saidimage intensifier tube, and an automatic brightness control circuiteffective to reduce said differential voltage in response to a currentsignal from said image intensifier tube.
 4. The device of claim 3further including a laser light source for projecting a pulse of laserlight into the scene, a laser range finder control logic circuit, saidlaser range finder control logic circuit having an input to said voltageconverter circuit effective upon operation of a laser range findingcommand signal to temporarily discontinue reduction of said differentialvoltage on said microchannel plate during a certain time interval. 5.The device of claim 4 wherein said laser range finder control logiccircuit includes a microprocessor-based circuit implementing ahigh-speed timer, and a range calculator for laser range findingoperations by use of said pulse of laser light.
 6. A day/night viewerapparatus, said apparatus comprising:an image intensifier tube providingan image having a brightness level; a power supply circuit for saidimage intensifier tube, said power supply circuit including a pair ofalternative means for controlling brightness of said image provided bysaid image intensifier tube, one of said alternative means beingoperational in a night-time imaging mode, and the other of saidalternative means being operational in a day-time imaging mode,respectively; said one alternative means of said pair including avoltage converter circuit providing a differential voltage on amicrochannel plate of said image intensifier tube, and a control circuitresponsive to a current level from said image intensifier tube tocontrol image brightness of said tube by selective reduction of saiddifferential voltage; said other alternative means of said pairincluding a pair of voltage source circuits, one of said pair of voltagesource circuits providing a negative voltage and the other providing avoltage which is positive relative to a first face of said microchannelplate, a switching network alternating connection of said photocathodeof said image intensifier tube between said pair of voltage sourcecircuits in a duty cycle.
 7. The apparatus of claim 6 further includingmanually-adjustable means for allowing a user of the device to adjustsaid duty cycle to be applied in said day-time mode of operation.
 8. Theapparatus of claim 6 further including a laser light source forprojecting a pulse of laser light from the apparatus toward an objectthe range to which is to be determined, a portion of the projected laserlight illuminating the object and being reflected back toward theapparatus; means for momentarily interrupting imaging operation of saidimage intensifier tube and also of brightness control for said imageprovided by said intensifier tube and operating said image intensifiertube in a high-response and high-gain condition respectively at saidphotocathode and microchannel plate;means for detecting an electronpulse produced within said image intensifier tube in said high-responseand high-gain condition in response to said selected portion of saidlaser light pulse; a timer measuring an time interval from projection ofsaid laser light pulse until said electron pulse, and a calculatordetermining the range from the apparatus to the object using said timeinterval and the speed of light as a measuring standard.
 9. A method ofoperating a viewing device in order to provide an image of controlledbrightness both during day-time and during night-time modes ofoperation, said method comprising steps of:providing the device with animage intensifier tube, and directing light from a scene to the imageintensifier tube; causing the image intensifier tube to responsivelyprovide a visible image; providing a power supply circuit for said imageintensifier tube, and including in said power supply circuit a pair ofalternative circuit means for controlling brightness of said image,making one of said alternative means operational in a night-time imagingmode, and making the other of said alternative means operational in aday-time imaging mode, respectively; including in said one alternativemeans a voltage converter circuit providing a differential voltage on amicrochannel plate of said image intensifier tube, and a control circuitresponsive to a current level from said image intensifier tube tocontrol image brightness of said tube by selective reduction of saiddifferential voltage; including in said other alternative means a pairof voltage source circuits, one of said pair of voltage source circuitsproviding a negative voltage and the other providing a voltage which ispositive relative to a first face of said microchannel plate, andalternating connection of said photocathode of said image intensifiertube between said pair of voltage source circuits in a duty cycle. 10.The method of claim 9 further including the steps of:projecting a pulseof light into the scene, and causing a portion of this pulse of light tobe reflected from an object in the scene to the image intensifier tube;in response to the reflected portion of the pulse of light causing saidimage intensifier tube to provide an electrical output; measuring a timeinterval between projection of said pulse of light and said electricaloutput indicative of a range from the device to the object: duringprojection of said pulse of light discontinuing control of imagebrightness from said image intensifier tube, and in anticipation ofreceipt of said reflected portion of said pulse of light, increasingresponse of said photocathode and gain of said microchannel plate inorder to produce said electrical output.
 11. The method of claim 10further including the step of resuming brightness control of said imagefrom said image intensifier tube after receipt of said reflected portionof said light pulse.
 12. A method of controlling image brightness froman image intensifier tube in imaging operation, and of alternativelyalso using said image intensifier tube in a high-response and high-gainmode as a detector for laser light reflection in order to measure arange to an object in both day-time and night-time, said methodcomprising steps of:providing a power supply circuit selectivelyproviding in a night-time imaging mode of operation a variabledifferential voltage to a microchannel plate of the image intensifiertube, and reducing said variable differential voltage in response to acurrent level from said image intensifier tube indicative of an imagebrightness above a desired value, and providing a power supply circuitselectively providing in a day-time imaging mode of operationalternating connection of a photocathode of said image tube to a pair ofdiffering voltage levels in a duty cycle; controlling brightness of animage provided by the image intensifier tube to a user of the device byselectively operating said power supply circuit alternatively in one ofsaid night-time and day-time modes of operation; projecting a pulse oflight to the object and causing a portion of this pulse of light to bereflected from the object to the image intensifier tube; temporarilysuspending the respective one of said night-time and said day-timeimaging mode of operation, and applying a high-response voltage level tosaid photocathode while also applying a high-gain differential voltageacross said microchannel plate; utilizing said image intensifier tube toprovide an electrical output in response to receipt of the reflectedlight; measuring a time interval from projection of said pulse of lightuntil provision of said electrical output by said image intensifiertube; from said time interval determining the range to the object usingthe speed of light as a measuring standard; and resuming the respectiveone of said night-time or day-time imaging operations.
 13. A method ofproviding day/night viewing of a distant scene with controlled imagebrightness in both day-time and at night-time, and of providing laserrange finding to an object in the distant scene, said method comprisingsteps of:receiving light from the distant scene; causing an imageintensifier tube to responsively providing an image replicating thescene; operating the image intensifier tube with a power supplyincluding a pair of alternative means for controlling brightness of saidimage, during night time operating one of said alternative means andduring day time operating the other of said alternative means; includingin said one alternative means a voltage converter circuit, and utilizingsaid voltage converter circuit to provide a differential voltage on amicrochannel plate of said image intensifier tube; providing a controlcircuit responsive to a current level from said image intensifier tubeto control brightness of said image in night-time mode by selectivereduction of said differential voltage; including in said otheralternative means a pair of voltage source circuits, utilizing one ofsaid pair of voltage source circuits to provide a negative voltage andutilizing the other of said pair of voltage source circuits to provide avoltage which is positive relative to a first face of said microchannelplate; providing a switching network, and utilizing said switchingnetwork to alternate connection of said photocathode of said imageintensifier tube between said pair of voltage source circuits in a dutycycle to control brightness of said image in day-time mode; projecting alaser light beam into the scene, suspending image brightness control inboth day-time and night-time mode, and applying a high-response voltageto said photocathode while also applying a high-gain voltage to saidmicrochannel plate; utilizing said image intensifier tube to produce anelectrical response to reflected laser light from an object in thescene; utilizing said electrical response to measure a time intervalindicative of range between the device and the object; and resumingimage brightness control after a predetermined interval allowing saidimage intensifier tube to produce said electrical response to reflectedlaser light from said object.